Recently, lipsticks that are soft to the touch and highly glossy are demanded in the market. In order to embody such demanded quality, back filling technique, that is, a manufacturing method including turning a container upside down, directly filling the inside of the container with a heat-melted cosmetic through a filling hole in the bottom, then cooling the cosmetic to solidify, thus molding a stick-type cosmetic, is advantageous and commonly carried out. In this method, generally, in a cylindrical portion (sleeve) that is a part of the container, a cylindrical cosmetic holder that can move up and down within the cylindrical portion is installed, and the inside of these cylindrical members is directly filled with a heat-melted cosmetic (bulk), which is then cooled in that state to solidify (Patent Literatures 1 and 2).
Since the sleeve and the holder are directly filled with the cosmetic molded by such a back filling technique, a part of the cosmetic after solidification may adhere to an inner wall surface of the sleeve of the container. When the cosmetic installed on the holder is moved up at the start of use, such adherence may cause high downward stress (in the direction toward the bottom) to act on the cosmetic. Also, in normal use for application, the distal end of the cosmetic is pressed by an object to be applied and therefore downward stress on the cosmetic is generated. Such downward stress acts as a force which withdraws the cosmetic downward from the cylindrical holder. Therefore, in order to prevent this, measures need to be taken to hold and fix the cosmetic on the holder. A common method for this is to provide one or a plurality of protrusions (ribs) such as pawl portions on the inner wall of the holder, load and solidify the melted cosmetic, and engage and hold the cosmetic with the ribs (Patent Literature 3).
However, the method of engaging and holding the cosmetic with the ribs has the following problem. That is, on the cosmetic molded by the back filling technique, stress is generated by the adherence of the cosmetic to the inner wall surface of the sleeve of the container during the moving-up action as described above. Such stress consequently concentrates on the engagement holding part between the cosmetic and the holder, that is, the rib portions.
In the engagement holding of the cosmetic via the ribs, the holding strength is secured by the hardness of the solidified cosmetic itself. Therefore, with a soft cosmetic, the holding strength in the holder via the ribs deteriorates, and sufficient holding cannot be realized if stress as described above is applied. Particularly, if, for example, a softer touch in the use of a stick-type cosmetic such as a lipstick is obtained by reducing the content of solid oil that forms the structure, the cosmetic itself becomes fragile. Therefore, in the conventional type of holder that holds the cosmetic with the ribs, the problem is that when stress concentrates on the engaged portion with the ribs as described above, the cosmetic in that part collapses and the cosmetic is not sufficiently held on the holder.
As a countermeasure against this, the engagement holding strength may be improved by increasing dimension including the size, length, and height of the ribs. However, there is an intrinsic characteristic of ribs such that, when filling the inside of the holder with the heat-melted cosmetic, the presence of protrusions such as ribs within the holder may cause disturbance in the flow of the melted cosmetic in the surrounding part, leaving air bubbles in the surrounding part after the filing is completed. Then, since the molten cosmetic begins to cool down immediately as it is loaded, and also due to the intrinsically low fluidity of the molten cosmetic, the cosmetic is consequently cooled and solidified with the air bubbles remaining near the ribs and forming cavities. The cavities around the ribs lower the engagement holding strength of the ribs on the cosmetic and may cause molding defects. Increasing the dimension of the ribs facilitates the generation of such air bubbles and increases the incidence of molding defects. Therefore, this is not sufficient as a method for improving the holding strength, particularly for a stick-type cosmetic with a soft touch and low mechanical strength.
As described above, damage and molding defects of the cosmetic on the rib portions become a further cause of a deterioration of the engagement holding strength of the holder with respect to a stick-type cosmetic, particularly, a stick-type cosmetic with a soft touch and low mechanical strength. Consequently, there is a disadvantageous that that the movement of the holder and the movement of the cosmetic do not interlock with each other or the cosmetic is pushed down in use, or the like. Furthermore, not only in normal use for application but also when the container is accidentally dropped and subject to a strong external impact, the cosmetic may fly out of the holder, damaging the surface of the cosmetic.
Patent Literature 4 discloses a configuration in which, though not for a cosmetic formed by the back filling technique, ribs as protrusions are formed in a spiral direction, thus enhancing the fitting strength with a middle tray (holder) so that the cosmetic is less likely to come off.
However, in this configuration, since the ribs are continuously formed in a spiral form, air bubbles are more likely to be generated near the ribs, posing the risk of molding defects if this is applied to a cosmetic formed by the back filling technique. Also, since stress is applied in a concentrated manner on the rib portions, there is a possibility that breaking starts at the rib portions, particularly in the case of a stick-type cosmetic with a soft touch. Moreover, since the stick-type cosmetic is required to be screwed in, the resistive force of the ribs that prevents the movement of the cosmetic in the rotating direction is not sufficient.
Thus, in order to solve the foregoing problems, the present applicant has invented a stick-type cosmetic holder which is formed in a cylindrical shape opened at the upper and lower ends and in which taper that gradually decreases the inner diameter from the upper opening side to a substantially central part is provided on the inner peripheral surface and a plurality of step portions are provided annularly on the inner peripheral surface where the taper is provided so that the substantially central part is higher than the upper opening side, with the step portions being formed with an inclination in relation to the axial center of the cylindrical shape as viewed from the lateral side (Patent Literature 5). That is, in this stick-type cosmetic holder, stress in vertical directions applied on the stick-type cosmetic held therein is received by the inner peripheral surface where the inner diameter of the holder is gradually decreased to form the taper (hereinafter referred to as a tapered surface) and stress in the directions of rotating the stick-type cosmetic within the holder is received by the step surfaces of the step portions, thus enabling secure holding of the stick-type cosmetic.
By the way, while such a stick-type cosmetic holder has no particular problems with a soft cosmetic as described above, the following problem may be considered when the cosmetic has normal hardness. That is, in order to realize a cosmetic with typical hardness, the content of wax needs to be increased. However, the rate of contraction of the cosmetic due to the cooling and solidifying when molding is known to rise with increase in the content of wax. Also, in the stick-type cosmetic holder of the invention of the applicant, since a plurality of step portions provides high holding strength, the cosmetic cannot properly contract within the cosmetic holder. Consequently, there is a possibility that damage such as cracks may occur partly in the cosmetic.    Patent Literature 1: JP-A-2001-87033    Patent Literature 2: JP-A-2002-349    Patent Literature 3: JP-A-2009-226004    Patent Literature 4: JP-A-2001-186920    Patent Literature 5: Japanese Patent Application 2010-171984